Analytical instrument providing corrected sample volume dependent parameter

ABSTRACT

The invention provides a device for extraction of a defined sample volume from a larger sample volume. The device includes a body having a reference surface and a measuring cavity extending from a part of the reference surface into the body, thereby forming at least one opening plane substantially uniform with the reference surface. An information carrier is applied to or distributed with the device, having direct or indirect volume information about defined volume established for the cavity. The invention also relates to a method for determining the volume of such a cavity, to a set of at least two such devices, to a method for dilution of at least two liquid samples by using at least two such devices, to an analytic instrument, to a method for operating such an instrument, to a system including the device and the instrument, and to a method for operating the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of patent application Ser.No. 12/444,394, filed on 5 Apr. 2009, now U.S. Pat. No. 8,033,186 B2,issued 11 Oct. 2011, which is a U.S. national phase of PCT applicationNo. PCT/SE2007/000833, filed 24 Sep. 2007, which claims the benefit ofSwedish patent application 0602104-2, filed 6 Oct. 2006. Priority of thefiling date of the parent applications is claimed, and the disclosuresof the parent application are incorporated herein by reference in theirentireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a device for extraction of a definedsample volume from a larger liquid sample volume, to methods fordetermining the volume of at least one cavity of a device, to a set ofat least two devices for dilution of liquid samples to the same ordifferent defined degrees, to an analytic instrument for operativeconnection to a sample measuring and diluting device having at least onemeasuring cavity, and to a system having a sample measuring and dilutingdevice and an analytical instrument.

2. Description of Related Art

In one type of blood testing, a system comprising a blood cell countingapparatus/analytical instrument provided with a blood sample volumedefining device, preferably in the form of a disposable cassette, isused. To be able to count the blood cells in an accurate and repeatableway it is of crucial importance to define an accurate volume of a bloodsample. The accurately defined volume of blood sample is normallydiluted by an accurately defined volume of a diluent or a lysing agent,in order to obtain a dilution ratio of typically 1:100 to 1:80000. Whencounting white blood cells is concerned the dilution ratio is typically1:400 and when counting red blood cells is concerned the dilution ratiois typically 1:40000, in the latter case the dilution often taking placein two steps. Thus, it is obvious that variations in sample volumes anddilution liquid volumes must be minimized such that a correct degree ofdilution and counting of blood cells always can be guaranteed.

Apparently, obtaining the same sample volumes are a critical step in thedilution procedure, since the volumes concerned are extremely smallcompared to the corresponding diluent volumes. To be able to obtain anaccurate dilution ratio of a blood sample it is of crucial importancethat the cavity in which the blood sample is contained is filled in avery precise and accurate and repeatable way, and that the variationsregarding the volume between different cavities having the same nominalvolume are made as little as possible.

The Swedish patent application No. 0303157-2 describes a method and adevice for defining a small volume of a larger liquid sample. The deviceincludes a first body and a second body. In a surface thereof, the firstbody has at least one cavity having said defined volume, and the secondbody includes an edge relatively slidable along said surface and overthe cavity thereby separating an excessive volume of sample from saidsurface, leaving a defined volume within the cavity.

By the non-published Swedish patent application No. 0500784-4 a samplevolume defining device is known which comprises a sledge and aframework, movable relative to each other. The device forms a part of adisposable support, preferably in the form of a cassette, and theframework is formed integrally with said support. The support comprisesat least two chambers, one of which is filled with an accurately definedvolume of diluent or lysing agent for dilution of a liquid sample,preferably a blood sample, and the other is empty and thus used forachieving the dilution and mixing of the liquid sample. At least oneaccurately defined cavity is made in the sledge. The components of thedevice are preferably made by injection molding.

Although all due care is take when said at least one cavity is made inthe first body/sledge, which in the description below is called asampling body/body, its volume will on one hand differ from samplingbody to sampling body made by the same molding tools as the tools wear,and so forth, and on the other hand from molding tools to molding tools.By knowing this volume variation between different cavities made indifferent sampling bodies, it is thus possible to even further improvethe accuracy of the blood analyses when performing blood cell counting.

SUMMARY OF THE INVENTION

The object of the invention is to take these volume variations of thecavities into consideration when performing the blood analyses. Thisobject is achieved by the devices, methods, and systems describedherein.

BRIEF DESCRIPTION OF THE DRAWINGS

A non-limiting example of the present invention will be describedhereinafter with reference to the accompanying drawings, wherein:

FIGS. 1 a and 1 b are schematic sectional views showing the principle ofa known device for extraction of a sample volume from a larger volumeaccording to the invention shown in a first and a second position,respectively;

FIG. 2 is a perspective view schematically showing a first principalembodiment of the known device;

FIG. 3 is a similar view showing a second principal embodiment of theknown device;

FIG. 4 is a similar view showing a third principal embodiment of theknown device;

FIG. 5 is a schematic view of a molding machine with four molding toolsshowing the manufacturing of a device for extraction of a sample volumefrom a larger volume according to the invention provided with twocavities, inherently said cavities having small variations in volume;

FIG. 6 shows a blood test taken from a the finger of a person to betransferred to a blood testing cassette to be placed in a blood cellcounting apparatus (schematically shown); the cassette being providedwith a volume variation information carrier;

FIG. 7 is a flow chart describing the different steps carried out fromobtaining the sampling bodies with cavities to the blood analysesconducted; and

FIG. 8 is another flow chart describing the different steps carried outfrom obtaining the sampling bodies with cavities to the blood analysesconducted.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS OF THE INVENTION

As indicated above, a sample volume defining device is known from WO2005/052553 and the co-pending application SE 0303157-2, bothincorporated by reference herein. Basically the known volume definingprocess incorporates a) application of a relatively larger, oftenundefined, volume of the sample, preferably liquids, onto a surface andinto a cavity formed in the surface and b) moving a scraping edge overthe surface to leave a smaller defined volume of the sample in thecavity. Further processing steps may follow, such as c) flushing thecavity with a liquid diluent, or dilution media, such as a solution orreagent, to obtain a diluted sample, d) mixing the sample and diluent toobtain a homogenous diluted sample and e) performing measurements on thediluted and mixed sample. The current invention builds on this knowntechnology and represents a development thereof.

For purposes of discussion the surface can be regarded as a referencesurface, comprising the physical surface as well as an “imaginary”surface, defining an opening plane for the cavity, the surface beingflush and continuous with the physical surface, or defined in mechanicalterms by movement of a thought entirely rigid scraper means in contactwith the surface, across the cavity, also referred to as a “measuringcavity” herein, so as to define a volume of the cavity limited by theimaginary surface. The reference surface shall at least surround thecavity to such an extent as to allow the scraping action and preferablythe reference surface encircles the cavity on all sides.

The reference surface may have different shapes as long as it meets thecontinuity requirement, consistent with the scraping purpose. Forexample, the reference surface with its cavity may be double-curved,meaning that it cannot be formed by bending a flat surface, asexemplified with a cavity in a ball valve, or the reference surface maypreferably be single-curved, meaning that it can be formed from a flatsurface, as exemplified by a cavity in a cylinder valve, or mostpreferably it is substantially flat, as exemplified by a cavity in aslide valve.

The cavity size, i.e. the volume under the imaginary surface, or ratherthe practical surface to be further discussed below, depends on severalfactors. Some of these factors are application dependent, such as samplenature and necessary volumes for planned dilution degrees orrequirements for intended measurement. In disposable devices, foreconomical, reasons it is generally desirable to minimize the volumes inorder also to minimize other features such as diluent volumes, mixingarrangements etc. However, manual manipulation and manufacturingconstraints, e.g. molding of plastics, may place a lower limit onpractical or possible cavity sizes. In case of several cavities, e.g.for different dilution degrees, the restrictions typically are set bythe smallest cavity. General values are difficult to give but experiencehas indicated that the cavity volume should preferably be larger than0.01 microliter (μl), preferably larger than 0.05 and most preferablelarger than 0.1 microliter. The maximum cavity volume can be kept below50 microliter, preferably below 25 and most preferably below 15microliter.

Similarly cavity shape may be determined by several factors. Besidesmanufacturing constraints that may place limits on advanced features ofsmall cavities, desirable shape is mainly dictated by efficient fillingand foreseeable, also expressed herein as reproducible, scrapingresults, of particular importance between different disposable devices.

Cavity filling may take place in various ways. As indicated, if a samplesurplus is simply placed on the cavity there is a risk for gas inclusionand unfilled voids in the cavity. To avoid this, the sample may beforced into the cavity, e.g. by a sample stream positively pumped byforced flow past the cavity, which, however, does not entirely securesflow through the cavity. Preferably then forced filling is made byinsertion of a probe straight above or into the cavity, preferably withcare taken against probe outlet contact and blocking, which cannoteasily be compensated by increased injection pressure due to thehydraulic area relationship, and with necessary precision care neededfor small cavities. For reasons given in the references a preferredfilling method is use of capillary forces for filling. The criteria forcapillary filling shall be regarded satisfied, and accordingly testable,if filling takes place, or can take place, without other forces applied.

The cavity may have several openings, or entrances, e.g. the cavity mayform a tube extending between two openings as in known capillary tubesalthough here also connecting to a capillary driven filling channel. Itis preferred, however, that to the extent the channel has more than oneopening these opens into one and the same reference surface. Mostpreferably the cavity has only one opening for best filling and scrapingproperties.

A sloping arrangement is consistent with a cavity design narrowing awayfrom the reference surface and, in case of cavities with only oneopening, towards its bottom or, differently expressed, thatcross-sections taken parallel with the reference surface have decreasingcavity areas when moving away from the reference surface, at least overa part of the cavity depth and preferably over substantially the cavityfull depth. It is further preferred that the cavity walls are at leastsubstantially perpendicular but preferably converging towards the cavitybottom, the bottom being the end farthest away from the referencesurface. Most preferably small or no undercut parts are present in thecavity.

Discussing next the scraping, the imaginary surface has been describedabove as an idealized surface entirely continuous with the referencesurface. However, in practice any scraping device able to be kept ingood contact with the reference surface must have a certain resilience,preferably the minimum resilience necessary for dynamic adaptation tothe reference surface, which is preferably made of a harder material,without undue further deformation. Certainly the material in thescraping device should not be soft, in the sense that it easily deformspermanently. Suitable materials may include thermoplastics andpreferably elastomers. The scraper resilience means that it will expandby deflection to a certain extent into the cavity volume, therebycreating an actual, or “practical” surface, defining the cavity openingplane for the cavity, generally so as to reduce the cavity volumesomewhat. This may not be a problem as long as the reduction ispredictable and foreseeable. In order to facilitate such predictabilityit may be of interest to minimize the volume deviation between theimaginary and practical surfaces, e.g. by having a limited resilienceand having a large enough area to cover the entire opening plane so asto entirely cover the cavity opening during some phase of the scrapingaction.

In summary, in order to strike a balance between the cavity shape designdictated by filling and the design dictated by scraping, it is preferredthat the cavity has an elongated opening surface and that the fillingdirection and the scraping direction have at least a vector component incommon, preferably a longer vector component in common and mostpreferably are substantially parallel. It is further preferred that atleast the up-flow, and scraping entrance, cavity end wall has a slowslope whereas other cavity wall are steeper. As indicated, all theseobservations apply more to larger cavities than to smaller cavities.

Independent of measuring cavity design it is of critical importance toestablish true cavity volume so as to enable correct dilution degree andin the end a reliable particles per volume count for a given testsample. Use of a measuring cavity under a reference surface as describedmakes it difficult to calibrate and utilize only a part of the cavityform measurement, e.g. by level or flow sensors as in alternativemeasuring methods. Further, when reusing one and the same measuringcavity, e.g. when the cavity forms a part of a reusable measuringinstrument, it might be sufficient to measure the cavity once and forall, and calibrate an instrument accordingly, especially if the reusedcavity body is designed in high quality materials such as hard metals orceramics. However, in disposable devices low cost materials are normallyselected and random factors, such as temperature or material lotvariations, as well as trend factors, such as manufacturing tool wear,tend to create variations in cavity volumes between different, or withina set of, disposable devices. Control over such variations then becomescritical for measurement quality.

Various methods can be used to “measure” a cavity volume. The volume canbe measured under the “imaginary” surface, e.g. by laser scanning ofcavity three-dimensional extension with integration of volume. Thevolume can preferably be measured under a “practical” surface asdiscussed, e.g. by filling a liquid of known particle concentration suchas a latex solution into the cavity followed by scraping, possibly byoptional dilution, for final counting of particles in knownconcentration.

As used herein “established” volume has a meaning different from“measured” volume, although established volume is always derived fromsome kind of measured or “calculated” volume. Certainly each cavity canbe measured and the measurement used as established volume also in asystem of multiple disposable devices, also referred to herein as a setof “cassettes”. However, the volume can also be “estimated”. For exampleit might be sufficient with measurements on less than all cavities in aset of cassettes. If, for example, the cavity bearing parts of thecassettes are of high quality and the corresponding manufacturing toolsare wear resistant it might suffice to measure one or a few cavityvolumes from each manufacturing tool, or tool part, and rely on this orthese measurements as established values for all cavities from the samemanufacturing tool or tool part. In case of less high quality materialsor long production series from the same tools it is preferred to derivea manufacturing trend for the resulting cavity volumes, e.g. bymeasuring cavity volumes at intervals, regular or irregular, e.g. in theform of a function or interpolated values, and using the trend to derivean established volume for each individual cavity. Normally amanufacturing tool is worn down in repeated use, resulting in slowlyreduced cavity volumes. Finally, in case the manufacturing process andresulting products can be reliably modelled the established cavityvolumes can be based on “calculation”. In summary an established cavityvolume can be based on measurement, estimation or calculations, e.g. asexemplified.

When making measurements, in order to compensate for even small randomfactors, it is generally preferred to make several measurements andderive a mean, median or similar statistical volume value. This ismeaningful only if the volumes have the same nominal or target values,e.g. a volume spread less than 1:2, preferably less than 1:1.5, morepreferably less than 1:1.25, and most preferably less than 1:1.1. Suchcavity volumes can be presented not only as absolute values but also asdeviations from a target or nominal value, e.g. on an informationcarrier to be read by an instrument.

However, as indicated, a cassette may include cavities of quitedifferent nominal volumes, e.g. for the purpose of providing suitabledifferent dilution degrees for red and white blood counts respectively.This in contrast to the known alternative method of a serially dilutingof one and the same sample, first to lower dilution degree, suitable forwhite blood cell count, followed by dilution of a part, possibly againextracted in a measuring cavity, of the first dilution sample to asecond dilution degree, suitable for red blood cell count. In contrast,a parallel dilution to two different dilution degrees from two cavitysamples is simpler in terms of steps performed on the cassette.Certainly it is possible to dilute to different degrees from twocavities of the same nominal volume but it is preferred to use a smallercavity volume for the higher dilution degree in order to keep dilutionvolumes down on a disposable device. Accordingly it is preferred toprovide cavities of at least two, and possibly more, nominal volumes onthe cassettes of the invention.

The established cavity volume information can be used for differentpurposes. A main object of the present invention is to obtain reliableand “defined” dilution degrees for samples measured in the cavities. Inconnection with blood samples this is important e.g. to obtain trueparticle counts in the end. In principle dilution degree compensationfor cavity volume deviations can be made for example either by adding anadapted amount of dilution media, in order to obtain similar “target”dilution degrees from measuring cavities of different establishedvolumes, or by adding similar dilution media volumes to measuringcavities of different established volumes, to obtain different but“known” dilution degrees, e.g. for allowing recalculation of particlecounts. All this is most meaningful between cavities having the samenominal volumes, e.g. within the ranges exemplified above. For highdilution degrees exact volume measurement is more important for thesmaller volume part than the larger volume part and in connection withblood testing a blood sample is often diluted more than 10 times,commonly to more than 100 times and often to more than 1000 times oreven more than 10000 times, and the precision problems are more severein connection with direct dilution, in contrast to serial or stepwisedilution.

As indicated a preferred arrangement is to place the measuring cavity ona disposable device, preferably a cassette type of having furtherfeatures, designed for operative connection to a reusable instrumente.g. having measuring, data processing and/or actuating means, allexemplified in prior art, e.g. WO 03/044488 or WO 2004/045770. It isthen possible to provide the instruments with features suitable for thevolume compensation described, e.g. by being capable of adding to thesample on the device either an adapted amount of dilution mediaaccording to the “target” dilution degree method or by adding a standardamount of dilution media according to the “known” dilution degreemethod. In either case the instrument can extract the dilution mediaamount from a reservoir on-board or attached to the instrument or from areservoir on the cassette. Alternatively and preferably at least a partand preferably all of the dilution media is pre-filled on the cassette,again either a volume adapted to the established cavity volume for thatparticular cassette according to the “target” method or a standardamount according to the “known” method. Intermediate solutions are alsopossible such as pre-dilution on the cassette followed by final dilutionon the instrument.

In addition to features for adding dilution media, the cassette and/orinstrument parts may comprise arrangements for mixing such as forflushing the sample from the measuring cavity and homogenizing themixture, as known as such in the prior art. It is preferred that atleast flushing can be performed on the cassette and preferably also somehomogenizing although such features can also be provided on theinstrument.

It is preferred that the disposable device, having the measuring cavity,has an information carrier, either arranged for distribution with thedevice or preferably attached to the device. The information carrier maycontain information for human reading only, e.g. for manual correctionof test results, but preferably the carrier has information in machinereadable form, e.g. for reading by any device, and most preferably theinformation is readable by a reader on the instrument in acassette/instrument system, e.g. by being provided in the form ofmechanical structures, bar code, magnetic tape, RFID, data chip machinereadable text etc. The information can be of any kind, such as type oftest to be performed on the device, lot number, expiry date, measuringcavity nominal volume etc.

Preferred information for the present purposes is data relating tonecessary compensation for the measuring cavity volume. Such informationcan be general, e.g. whether or not a compensation action is at allneeded from a human operator or the instrument and accordingly which oneof several possible modes of operation is expected. For example, in caseof cassette onboard dilution media volume compensation, theoreticallyneither an operator nor the instrument needs to take any compensationaction. In case of dilution with a standardized dilution media volume arecalculation of measuring results may be needed. In case of partialdilution on the cassette a complementary dilution might be needed.Accordingly, in a set or population of disposable devices theinformation carrier can inform about the applicable compensation methodor mode of operation expected for each individual device. Withpreference the information carrier also includes data about themeasuring cavity established volume, which data can be presented in manymanners for example in the form of an absolute volume value or as adeviation from a nominal value. Such information can be used for any ofthe compensation method described above, e.g. independent of theinstrument for manual or external recalculation or dilution correction,but preferably for data transmission to the instrument for any of theexemplified instrument actions.

It is clear from the above examples that an operative connection betweendevice and instrument may include various features besides necessarymechanical compatibility. Features may be included for informationtransfer at least from the device to the instrument. Features may beincluded for transfer of liquid, e.g. sample but preferably dilutedsample and possibly rinsing liquid, at least from the device to theinstrument, e.g. for measurements, dilution, complementary dilution,mixing, rinsing of the instrument etc., but preferably also back to thedevice, e.g. for disposal of sample contaminated liquid such as dilutedsample and instrument rinsing liquid. Features may be included forinstrument actuation of device process operations, such as scrapingaction, flushing, mixing, liquid transfer to the instrument etc.

With reference to FIG. 1-5 c different embodiments of a known device forextraction of partial defined sample volume from a larger liquid samplevolume is shown. An information carrier (not shown) is applied to orarranged for distribution with said device.

FIGS. 1 a and 1 b show a first body 10 that has a reference surface 11in which is provided a cavity 12 having an accurately defined, smallvolume. A relatively large volume 13 of a sample, such as a bloodsample, is applied onto the reference surface 11 such that it is ensuredthat the cavity is filled with sample.

A second body, scraper, 14 has an edge 15 abutting the reference surface11 of the first body. The bodies 10 and 14 are relatively slidable alongthe reference surface 11 as indicated by an arrow A, so that the edge,upon passing the cavity, scrapes or shears off a volume 16 of the samplealong the reference surface 11 leaving just the accurately defined,small sample volume 17 within the cavity 12. This situation is shown inFIG. 1 b.

In practice, the second body 14 has a surface 18 starting at the edge 15and facing and abutting the reference surface 11 of the first body in afluid tight manner. For the purpose of diluting the accurately defined,small sample volume 17, two channels 19, 20 extend through the secondbody and open in its surface 18 at positions enabling respective fluidcommunication with the cavity 12 as shown in FIG. 1 b. The channels areshown here to extend in a V-shaped, converging manner towards thesurface 18. Evidently, the channels may extend in other directionstowards the surface 12 and the cavity 12 therein, including mutuallyparallel channel directions.

Conduits 21, 22, indicated by broken lines, connect a respective one ofthe channels 19, 20 with a respective one of receptacles 23, 24. Thereceptacle 23 is shown in FIG. 1 a to contain a defined volume of aliquid 25, such as a diluent or a lysing agent. When the first andsecond bodies are in the relative position shown in FIG. 1 b, flow fromthe receptacle 23 through the conduit 21 will be directed into thecavity 12, thereby flushing its volume 17 of sample and bringing itthrough the conduit 22 into the receptacle to provide therein a volumeof diluted sample having a defined dilution ratio. The volume of dilutedsample may be brought to flow several times forth and back between thetwo receptacles to ensure proper mixing and dilution, but tests haveshown that already one flushing provides a satisfactory result.

Depending on the kind of test to be performed and the dilution ratiodesired, the cavity may typically have a volume of between 0.05 and 10μl, even if it is quite possible to provide cavity volumes of, e.g.,between 0.02 and 20 μl.

In practice, it may be useful to provide more than one cavity in thesurface of the body 10, for instance one relatively small cavity (e.g.0.05 μl) and one relatively large cavity (e.g. 10 μl), thereby enablingsimultaneous dilution into two different dilution ratios. This is thepreferred embodiment of the invention as regards blood analysis.

Examples of prior art devices embodying this possibility are shown inFIGS. 2-4.

The embodiment of FIG. 2 comprises a block-shaped housing 25 (secondbody) having therein a slot 26. A slide 27 (first body) has in an upperreference surface 28 a smaller cavity 29 and a larger cavity 30. Theslot has an edge 31 closely abutting the surface 28. Two pairs ofconverging channels 32, 33 and 34, 35 extend through the housing 25 andopen in a surface of the slot 26 at respective locations correspondingto the positions of the cavities 29, 30. Thus, a non-shown, lager volumeof a sample applied onto the reference surface 28 will be sheared off bythe edge 31 upon sliding the slide 27 into the slot as indicated by anarrow B, leaving two accurately defined volumes of sample in thecavities 29 and 30 to be diluted as explained in connection with FIGS. 1a and 1 b.

In FIG. 3, the first body is a disc-shaped body 36 having in a referencesurface 37 a smaller cavity 38 and a larger cavity 39. The second bodyis likewise a disc-shaped body 40 having at its circumference a cut-outportion providing access to the surface 37 of the first body and alsoproviding at least one edge 41 abutting the reference surface 37. Twopairs of converging channels 42, 43 and 44, 45 extend through the body40 and open in its surface abutting the body 36 at respective locationscorresponding to the positions of the cavities 38, 39. Thus, anon-shown, lager volume of a sample applied onto the surface reference37 will be sheared off by the edge 41 upon relatively rotating the twobodies as indicated by an arrow C, leaving two accurately definedvolumes of sample in the cavities 38 and 39 to be diluted as explainedin connection with FIGS. 1 and 2.

In FIG. 4, the first body is a cylindrical body 46 having in itsperipheral reference surface 47 a smaller cavity 48 and a larger cavity49. The second body is a block-shaped body 50 having one surface 51concavely shaped in conformity with the cylindrical reference surface47. An edge 52 of the surface 51 abuts the reference surface 47. Twopairs of converging channels 53, 54 and 55, 56 extend through the body50 and open in its surface 51 abutting the body 46 at respectivelocations corresponding to the positions of the cavities 48, 49. Thus, anon-shown, larger volume of a sample applied onto the reference surface47 will be sheared off by the edge 52 upon relatively rotating the twobodies as indicated by an arrow D, leaving two accurately definedvolumes of sample in the cavities 48 and 49 to be diluted as explainedin connection with FIGS. 1 a and 1 b.

FIG. 5 shows schematically an injection molding machine 51 with fourmolding tools (not shown) for the manufacturing of sampling bodies 52 a,52 b, 52 c, and 52 d, each provided with at least one cavity. In theexample shown two cavities 53, 54 are provided in one sampling body.When molding sampling bodies the cavities will have small variations involume. One such sampling body forms part of blood testing cassette 65to be placed in an analytical instrument 60 (FIG. 6). Although, in thedescription below reference is made to a molding machine with fourmolding tools, it is obvious for the man skilled in the art that themolding machine can have 2, 4, 6, 8 or even more molding tools.

In the case the sampling body is provided with two cavities 53, 54 forsimultaneously counting both white and red cells, a cassette 65 isprovided with two chambers (not shown) filled with a dilution or lysingagent and two empty chambers (not shown), whereby one filled chamber isin fluid communication with one cavity of the sampling body filled withthe blood sample and one empty chamber. By this arrangement theaccurately defined blood sample can be mixed with the dilution or lysingagent and diluted to a dilution ratio range of about 1:100 to 1:80000within the cassette 65.

The typical nominal volume of the cavities 53, 54 in the sampling bodyis within the range of about 0.01-0.5 μl, preferably about 0.1 μl, andabout 1-10 μl, preferably 5 μl, respectively. Due to the large dilutionratio even small variations in the volumes of the cavities 53, 54 ofdifferent sampling bodies 52 a, 52 b, 52 c, 52 d will greatly influencethe result of the cell counting.

Although the volume of the cavities 53, 54 from each molding tools isapproximately the same during a batch of sampling bodies, the respectivecavity of sampling bodies 52 a, 52 b, 52 c, and 52 d will have differentvolumes.

To be able to carry out the invention a number of cavity volumes aremeasured so as to obtain volume information of the cavity volume sought.

According to the invention these variations in volume between cavitiesfrom different sampling bodies 52 a from the same molding tools and fromsampling bodies 52 a, 52 b, 52 c, and 52 d from different molding toolsare measured and used to improve the results of blood cell countinganalyses.

These variations in volume can also be expressed as, for instance, anabsolute volume value, a deviation from a nominal volume value of thesmall cavity and the large cavity, respectively.

Thus, according to the invention by knowing these variations in cavityvolume an established value of the cavity volume sought can bedetermined, and the cassette or blood sample volume defining device 65can thereby be provided with any type of volume information carrier 67,as seen in FIG. 6.

Thus, as seen in FIG. 6, a blood sample is taken from the finger of aperson by a syringe, for instance, and transferred to the device 65provided with the volume information carrier 67. The volume informationis coded in machine readable form, for instance, and comprises a barcode, a magnetic code, an electronic memory, machine readable text, aradio frequency identification device (RFID) or similar means, showingthe established value which can be read by any suitable arrangement. Thedevice 65 is then inserted into the instrument 60 and the well-definedvolume of the blood sample is diluted by and mixed with diluent and/orlysing agent to the desired dilution ratio.

Moreover, in another embodiment (not shown) the device is adapted to beconnected to an analytical instrument via conducting arrangements fortransferring sample and/or diluent containing liquid to the instrument.Also the volume information is transferred to the instrument by suitablemeans.

The information carrier 67 mentioned above is used for compensationvariations in the volume of cavities 53, 54 of different samplingbodies. Said information carrier 67 can also contain other informationsuch as batch number, best-before date, information about the type andvolumes of the diluent and/or lysing agent, and so forth.

To be able to perform the measuring it is necessary to define thephysical location and form of the opening plane. This is done on onehand by moving a scraper along and in contact with reference surfaceover the cavity, or on the other hand by interpolating the opening planefrom an optical detection of the reference surface surrounding theopening plane.

The measuring of the cavity can also be done by filling an excess liquidamount in the cavity and moving the scraper along and in contact withthe reference surface over the cavity, which liquid left in the cavityis then compared with a reference cavity of known volume.

Another way of measuring the cavity volume is by optical detection ofsaid volume and possible subtraction of the volume above the openingplane. Preferably the established volume is the measured volume value,or the mean value of the measured value.

Another possible way of estimating the cavity volume is to measure thechanging trend for several devices and assigning established volumevalues to the several devices based on the trend.

As is obvious for the man skilled in the art the measured volume valuecan be obtained for more than one cavity in the reference surface, andthe more than one cavity have the same nominal target volumes.Preferably, the measured volume values lie within a range of 1:2.

FIGS. 7 and 8, respectively, is a flow chart showing two differentaspects to carry out the invention.

In FIG. 7., showing the first aspect, sampling bodies 52 a, 52 b, 52 c,and 52 c with cavities 53, 54 are made by different molding tools byinjection-mold, for example, of a suitable plastic material. Thesampling bodies from the same molding tools are grouped and therespectively cavity of the sampling bodies is measured by known means soas to obtain an average volume or a value of the volume deviation of therespectively cavity of the samplings bodies from the same molding tools.

Then the sampling bodies are assembled with pre-formed frameworks,preferably made of the same plastic material as the sampling bodies, soas to form cassettes. At least one particularly dedicated chamber madein the framework is pre-filled with an accurate volume of diluent and/orlysing agent and has fluid communication through channels made in theframework and via the respectively cavity with at least one emptychamber made in the framework. Thus, by this arrangement it is possibleto mix the diluent and/or lysing agent with the blood sample in said atleast one cavity. Volume information carriers in the form of labelsprinted with exact volume information of the respectively cavity of theassembled framework are applied to the cassettes.

The cassettes are packed in suitable package material and distributedfor storage or to the final user.

The second aspect, shown in FIG. 8, differs from the first aspect inthat the frames and the sampling bodies are assembled together formingcassettes. The at least one chamber containing the diluent or lysingagent is filled with said agent to such an amount for obtaining theextent of dilution of the blood sample sought.

When a blood sample is to be take and analyzed the final user opens acassette, and the blood sample is introduced into the cassette by knownmethods as taught in, for instance, the non-published Swedish patentapplication No. 0500784-4, and at least one accurately defined bloodsample volume in the cavity of the body is obtained and brought intocommunication with the diluent and/or lysing agent in the cassette.

The cassette is then placed in the blood counting apparatus which mixessaid at least one accurately defined blood sample volume with thediluent and/or lysing agent. The apparatus counts the blood cells andreads the information regarding the exact volume of the cavity from thelabel, which information is used to calculate, by suitable means, thedilution ratio and thus the accurate blood cell concentration.Thereafter the cassette is removed from the apparatus and disposed of.

What is claimed is:
 1. An analytical instrument for operative connectionto a disposable sample measuring and diluting device having at least onemeasuring cavity for extraction of a defined volume from a larger volumeof a liquid sample, the instrument comprising: a measuring unit adaptedto measure a sample volume dependent sample parameter; electronicsadapted to process signals from the measuring unit; an input unitadapted to receive data directly or indirectly related to an establishedvolume value of the at least one measuring cavity of the disposabledevice, from an information carrier applied to or distributed with thedisposable device; and a correction arrangement adapted to compensatedifferences in the established volume value of the at least onemeasuring cavity of the disposable device to obtain a corrected samplevolume dependent sample parameter, when the disposable device is used onthe instrument.
 2. The instrument of claim 1, wherein the data is anabsolute volume value or a deviation from a nominal value.
 3. Theinstrument of claim 1, wherein the information carrier further includesdata reflecting a diluent volume in the disposable device for mixingwith the sample and/or sample dilution degree.
 4. The instrument ofclaim 1, wherein the correction arrangement comprises a calculatoradapted to provide a numerical compensation of differences in theestablished volume value.
 5. The instrument of claim 4, wherein thecalculator is adapted to interpret the data to decide whether thenumerical compensation is needed.
 6. The instrument of claim 1, whereinthe correction arrangement comprises a dilution controller adapted forpartial or full dilution of the sample extracted in the disposabledevice to a defined dilution degree.
 7. The instrument of claim 1,wherein the data related to the established volume value is coded inmachine readable form.
 8. A method for operating an analyticalinstrument with a disposable sample measuring and diluting device havingat least one measuring cavity for extraction of a defined volume from alarger volume of a liquid sample, the method comprising: operativelyconnecting the disposable device to the instrument, said instrumentcomprising a measuring unit adapted to measure a sample volume dependentsample parameter, and electronics adapted to process signals from themeasuring unit; inputting or presenting to the instrument data directlyor indirectly related to an established volume value of the at least onemeasuring cavity of the disposable device from an information carrierapplied to or distributed with the disposable device; and performing acorrection for compensation of differences in the established volumevalue to obtain a corrected sample volume dependent sample parameter onthe instrument.
 9. The method of claim 8, wherein the data is anabsolute volume value or a deviation from a nominal value.
 10. Themethod of claim 8, the data related to the established volume value iscoded in machine readable form.
 11. The method of claim 8, wherein thecorrection provides a numerical compensation of differences in theestablished volume value.
 12. The method of claim 8, wherein thecorrection comprises interpretation of the data to decide whether anumerical compensation is needed.
 13. The method of claim 8, wherein thecorrection comprises providing a volume of a dilution media according tothe established volume value of the at least one measuring cavity toachieve a target dilution degree.
 14. A system comprising: (i) adisposable sample measuring and diluting device comprising at least onemeasuring cavity for extraction of a defined volume from a larger volumeof a liquid sample, and an information carrier, applied to ordistributed with the device, having direct or indirect volumeinformation about the defined volume established for the measuringcavity; and (ii) an analytic instrument comprising (a) a measuring unitadapted to measure a sample volume dependent sample parameter; (b)electronics adapted to process signals from the measuring unit; (c) aninput unit adapted to receive data directly or indirectly related to anestablished volume value of the at least one measuring cavity of thedisposable device, from an information carrier applied to or distributedwith the disposable device; and (d) a correction arrangement adapted tocompensate differences in the established volume value of the at leastone measuring cavity of the disposable device to obtain a correctedsample volume dependent sample parameter, when the disposable device isused on the instrument.
 15. The system of claim 14, wherein thedisposable device comprises a body having a reference surface and the atleast one measuring cavity extending from a part of the referencesurface into the body, thereby forming at least one opening planesubstantially uniform with the reference surface, the cavity having thedefined volume below said opening plane in said reference surface, thebody being adapted for reception of an excess sample volume at thecavity and elimination of sample above the reference surface to leave inthe cavity a measured sample volume having said defined volume.
 16. Thesystem of claim 14, wherein the data is an absolute volume value or adeviation from a nominal value.
 17. The system of claim 14, wherein theinformation carrier further includes data reflecting a diluent volume inthe disposable device for mixing with the sample and/or sample dilutiondegree.
 18. The system of claim 14, wherein the correction arrangementcomprises a calculator adapted to provide a numerical compensation ofdifferences in the established volume value.
 19. The system of claim 18,wherein the calculator is adapted to interpret the data to decidewhether the numerical compensation is needed.
 20. The system of claim14, wherein the correction arrangement comprises a dilution controlleradapted for partial or full dilution of the sample extracted in thedisposable device to a defined dilution degree.